The present invention relates generally to method and system for determining reference speed in a vehicle, and, in particular, to method and system for determining a reference speed indicative of true ground speed in a locomotive driven by electric traction motors.
Locomotives used for various transportation applications are generally equipped with speed sensors connected to individual traction motors. Information from these speed sensors is compared with a reference speed (e.g., an estimate of the true ground speed) for obtaining the maximum adhesion and for wheel slip/slide protection. The estimate of ground speed, or reference speed, relies on individual motor speed sensors along with other ground speed measurements, such as radar-based ground speed measurements. The use of radar to estimate ground speed has disadvantages due to cost, poor accuracy and misoperation under some ground conditions and other environmental conditions. Accordingly, there is a need in the art for a technique for estimating ground speed which does not use radar.
U.S. patent application Ser. No. 09/842,554, filed on Apr. 26, 2001, commonly assigned to the assignee of the present invention and herein incorporated by reference, describes innovative system and techniques that advantageously allow elimininating radar measurements in order to determine the reference speed of the vehicle. The system and techniques of the above-identified patent application are particularly useful for relatively heavy-haul applications since vehicular acceleration is presumed to be relatively constant between samples. In passenger and relatively light-load haul applications, the assumption of having a constant acceleration between samples may not be valid. In view of the foregoing issues, it would be desirable to provide system and techniques not premised on having a relatively constant acceleration between samples, and, as a result, can be advantageously used for vehicles configured for light inertia applications.
Generally, the present invention fulfills the foregoing needs by providing in one aspect thereof, a method for determining a reference speed indicative of true ground speed of a vehicle having a plurality of axles. The reference speed for a designated one of the axles is dynamically adjusted to account for changes in vehicular acceleration that may occur while determination of the reference speed is being performed. The method allows collecting a stream of samples over respective sampling intervals of at least one motion-indication parameter corresponding to a respective axle using a torque reduction rulebase configured to avoid high torque reduction, and inaccuracies in the motion-indication parameter due to high levels of creep, if any, in a wheel of the respective axle. The method further allows estimating an inertia value for the vehicle based on respective changes in tractive effort and acceleration over each sampling interval. The collected motion parameter samples are adjusted for changes in acceleration over each sampling interval using the estimated inertial value. A signal indicative of axle speed is limited to at least one respective limit value of rate and magnitude based on the inertially-adjusted parameter samples. The limited signal indicative of axle speed comprises the reference speed for the designated axle.
The present invention further fulfills the foregoing needs by providing in another aspect thereof, a method for determining inertial estimates of a vehicle during dynamic operation thereof. The method allows collecting a stream of samples over respective sampling intervals of at least one motion-indication parameter corresponding to a respective axle of the vehicle. The method further allows estimating an inertia value for the vehicle based on respective changes in tractive effort and acceleration over each sampling interval.
In another aspect thereof, the present invention provides a method for controlling torque applied to an axle of a vehicle while performing sampling of motion-indication parameters of that axle. The method allows collecting a stream of samples over respective sampling intervals of at least one motion-indication parameter corresponding to a respective axle using a multi-stage torque reduction rulebase. The method further allows configuring the multi-stage torque reduction rulebase to avoid high torque reduction, and inaccuracies in the motion-indication parameter due to high levels of creep, if any, in a wheel of the respective axle.
In yet another aspect thereof, the present invention provides a method for using an inertial estimate of a vehicle for adjusting at least one parameter indicative of vehicle motion. The method allows collecting a stream of samples over respective sampling intervals of at least one motion-indication parameter corresponding to a respective axle of the vehicle. The method further allows estimating an inertia value for the vehicle, and adjusting the collected motion-indication parameter samples for changes in acceleration over each sampling interval based on the estimated inertial value of the vehicle.
In still another aspect thereof, the method provides a system for determining a reference speed indicative of true ground speed of a vehicle having a plurality of axles. The reference speed for a designated one of the axles is dynamically adjusted to account for changes in vehicular acceleration that may occur while determination of the reference speed is being performed. The system includes a module configured to collect a stream of samples over respective sampling intervals of at least one motion-indication parameter corresponding to a respective axle using a torque reduction rulebase configured to avoid high torque reduction, and inaccuracies in the motion-indication parameter due to high levels of creep, if any, in a wheel of the respective axle. The system further includes an inertia estimator configured to estimate an inertia value for the vehicle based on respective changes in tractive effort and acceleration over each sampling interval. A module is configured to adjust the collected motion parameter samples for changes in acceleration over each sampling interval using the estimated inertial value. A limiter configured to limit a signal indicative of axle speed to at least one respective limit value of rate and magnitude based on the inertially-adjusted parameter samples. The limited signal indicative of axle speed comprises the reference speed for the designated axle.